IIRC these sources were already released under a permissive license along with their driver distribution. This just seems to be them putting those sources on GitHub and being more open to contributions.
On quick inspection, this is a complete, MIT-licensed kernel driver.
My understanding as well was that the bulk of the kernel space driver was previously only available as a binary blob, with only a small shim layer open sourced that loaded the rest of the kernel module and translated all of the internal kernel calls. I heard a rumor this was actually core to their internal legal theory about why they could have a binary blob kernel driver.
Required firmware blobs and the user space libraries are ultimately different components in the stack.
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/lin...
It would not be much of a stretch at all for nvidia to include their firmware there.
The userspace stack is an issue. For upstream Linux, there’s a fairly hard rule that graphics driver interfaces must be usable with open source userspace. But I don’t think the nvidia graphics user parts are particularly secret, and someone could write such a thing.
But this is different, it's voluntary.